Photographic emulsions containing 2, 5-dimethoxytetrahydrofuran



Feb. 12, 1952 w. A. STANTON 2,585,596

FHOTOGRAPHIC EMULSIONS CONTAINING 2,5DIMETHOXYTETRAHYDROFURAN Filed Dec. 29, 1949 GELATINO SILVER HALIDE CONTAINING 2,5-DIMETHOXYTETRAHYDROFURAN PAPER BASE 4 v GELATINO SILVERHALIDECONTAINING Wm 2,5-DIMETHOXYTETRAHYDROFURAN FILM BASE INVENTOR:

WILLIAM ALEXANDER STANTON gjzm m;

ATTORNEY.

flayers over any extended period.

Patented Feb. 12, 1952 PHOTOGRAPHIC EMULSIONS CONTAINING 2,5 -DIME.THOXYTETRAHYDBQFURAN William Alexander .jStanton, 'Westfield, N. J., as- Signor {to E. I. du FPont de Nemours and Company, Wilmington, DeL, (a corporation of Delaware Application December 29, 1949, Serial No. 135,819

5 Claims.

methoxytetrahydrofuran and to their preparation.

An object of this invention is to provide photographic silver halide emulsions which have improved characteristics when coated in the form of thin light-sensitive layers. A further object is to provide protographic gelatino silver halide emulsions which form thin flexible layers which are hard, that is, have a relatively high melting point but are freefrom brittleness. Another object is to provide a simple .buteffective method of improving the hardness" of photographic gelatino silver halideemulsions. A furtherobject is to provide such a method which does not have a deleterious efiect on the coating characteristics of the prepared emulsions. Yet another object is to provide such emulsions which have no undesirable effects on the resulting developed images. Still other-objects willbe apparent from the following description of the invention.

Various aldehydes and aldehyde yielding compounds have been proposed for addition to gelatino silver halide emulsions *in order to increase their melting points. Thus formaldehyde, acetaldehyde and various dialdehydes, e. .g., glyoxal and mesoxaldeh-yde in monomeric and polymeric form have been proposed buthave-numerous disadvantages." Thus formaldehyde is quite toxic and an irritant and constitutes a health hazard solid crystallizes if too 'high concentrations are added to the molten emulsion.

Succindialdehyde has been found to be unattractive for such use because it is quite unstable and readily polymerizes. Ithasarelatively high reaction rate making the coating of a paper, giilm, etc, support rather difficult because the emulsion thickens and cannot be coated in thin uniform in addition, gelatino silver halide emulsions which contain 2 succi-ndialdehyde do not result in uniform coatings "and repellant spots are formed which cannot be uniformly overcoated, e. g., with a protective gelatin layer. The developed films have high fog and a yellow stain which is decidedly disadvantageous.

It has been found that if small amounts of 2,5-dimethoxytetrahydrofuran are added to .a photographic gelatino silver halide emulsion the disadvantages of the compounds described above are obviated and a number of technical advantages .are obtained. The compound apparently slowly reacts with the gelatin and 'hardens it. This reaction is not noticeable during the preparation of the emulsion nor durin the coating of the fiowable emulsion onto a support such as .a paper base or .a film base. However, upon drying and aging of the resulting photographic elements a beneficial hardening action takes place without any deleterious photographic effect on the .emulsion. Whilean excellent hardening action is obtained and the melting point of the coated emulsion .layer is raised ,a substantial amount the layers do not become brittle but retain a high degree of flexibility. The resulting photographic elements are shown in the accompanyin-g drawing wherein:

Fig. 1 is an enlarged cross-sectional view of a paper base coated with the novel emulsion; and

Fig. 2 is an enlarged cross-sectional view of a film base coated with the novel emulsion.

Referring now to Fig. 1 apaper base I carries gelatino silver halide emulsion layer 2 which contains 2,5-dimethoxytetrahydrofuran. In Fig. 2

=film1base 3 carries gelatino silver halide emulsion layer Awhich contains 2,5-dimethoxytetrahydrofuran.

The 2,5-dimethoxytetrahydrofuran can be added to the emulsion over a fairly wide range of amounts, e. g., 5 to 30 milliliters per 100 grams of gelatin (dry basis) and preferably 6 to 12 milliliters per 100 grams of gelatin.

The invention will be further illustrated but is not intended to be limited by the following examples:

Example I A gelatin silver chlorobromide emulsion containing 6.3% gelatin was made in the normal manner and divided into one liter portions. Sampie 1 contained no hardener. To sample '2 there was added 5.5 milliliters of a 6.68% solution of formaldehyde and 5.6 milliliters of a 6.68% "solution of chrome alum. To three other one liter portions there were added 4, 8 and 16 milliliters respectively of 2,5-dimethoxytetrahydrofuran. The test samples were then coated onto a barytacoated paper base and dried in the normal manner. The table below sets forth the melting point and flexibility comparison figures for these samples at three stages of aging, namely, when freshly coated, 14 days and 21 days after coating. The melting point is determined by immersing a strip of the coated layer in a water bath and slowly raising the temperature of the bath until the emulsion is observed to melt. The flexibility is determined by bending a strip of the emulsion coated element over an acute edge away from the emulsion coated side. The number of degrees away from the normal plane of the strip at which the emulsion layer is observed to fracture is taken as a measure of flexibility.

Test rim Point ggg Flexibility Fog Degrees Degrees Degrees The fog values in the above table were obtained by exposure and development of the film in the conventional manner, e. g., exposure for 8 seconds and development in a standard metal-hydroquinone paper developer at 68 F. for 1 minutes. It will be noted that the test paper containing dimethoxytetrahydrofuran was relatively free In the above table DMTHF is dimethoxytetrahydrofuran.

Example II A gelatino silver chloro bromide emulsion containing approximately 6% of gelatin was made in the usual manner and divided into one liter portions. Sample 1 contained no hardener and to samples 2, 3, 4, 5, 6, 7 and 8 there were added the proportions of the agents listed in the following table. The various test samples were then coated onto a baryta-coated photographic paper base and dried in the usual manner. The following table sets forth the melting point and flexibility comparison figures for these test samples when freshly coated and '7 days after coating with accelerated aging in an oven maintained at a temperature of 120 F. and a relative humidity of respectively:

- Fresh 7 days in oven Test Added Agent M. P Flex. M. 1?. Flex.

4 l None 95 85 180 78 2 Chrome Alum and Formaldehyde 125 82 200 3 8 ml. DlWITHF- 95 200 93 4 12.25 ml. Sucoin 205 80 200 89 95 73 200 77 Chrome Alum and 0' maldehyde 205 44 200 70 Relative Humidityper cent 54 44 In the above table DMTHF is dimethoxytetrahydrofuran. In test sample 8 the chrome alum was in the emulsion and formaldehyde in an overfrom fog, whereas, one containing succindialdehyde had material fog.

Tests were conducted with emulsions of the type described in Example II which contained in addition to the dimethoxytetrahydrofuran small amounts of photographic sensitizing dyes with similar results. Among these dyes are those described in U. S. Patents 1,950,876, 2,071,898 and 2,342,546. In was found that the dimethoxytetrahydrofuran did not have a deleterious eiiect on the sensitizing action on any of these dyes but succindialdehyde had an adverse effect on certain dyes in the last mentioned patent.

While the above examples are all limited to the addition of 2,5-dimethoxytetrahydrofuran to gelatino chloro bromide emulsions, the compound is not limited to use in this specific type of emulsion. To the contrary, it can be added to silver chloride emulsions, silver bromide emulsions, silver iodobromide emulsions, silver chloride iodide bromide emulsions and of the simple and mixed type in gelatin and other equivalent colloids. The emulsions, moreover, contain various types of sensitizing dyes, color formers and other commonconstituents of photographic emulsions. The 2,5-dimethoxytetrahydrofuran does not seem to have any deleterious efiect upon the usual types of emulsions used in photography. However, it does have an excellent hardening action, the effects of which are not immediately noticeable but are obtained upon aging of the resulting photographic elements.

The photographic elements described in the foregoing examples which contained the 2,5- dimethoxytetrahydrofuran were found to be free from yellow stain after exposure, development and fixing in the usual Way. Similar photographic papers containing free dialdehydes such as glyoxal and hydroxyadipaldehyde on the other hand had an undesirable yellow stain.

rials include paper, aluminum, polymethacrylic acid, methyl and ethyl esters, vinyl chloride polymers, polyvinylacetals, nylon, polyesters, e. g., ethylene glycol-terephthalic acid polymers, cellulose acetate, cellulose nitrate, cellulose propionate; etc.

An advantage of this invention resides in the fact that the satisactory hardening of photographic gelatino silver halide emulsions can be obtained in a simple yet effective manner. It has been found that when 2,5-dimethoxytetrahydrofuran is added to emulsions similar to those described above and coated onto film base or a baryta-coated paper base that a uniform, slow hardening action takes place. When an overcoat is applied to the gelatino silver halide emulsion containing the compound in question, the uniform overcoating is obtained. However, with other agents such as succindialdehyde repellent spots are produced due to an excessive hardening action so that uniform coating cannot be obtained and overcoatings do not uniformly adhere to the coated emulsion. A further advantage of the addition of 2,S-dlmethoxytetrahydrofuran to gelatino silver halide emulsions resides in the fact that this agent does not have a deleterious chemical effect upon sensitizing dyes. Formaldehyde and compounds containing formaldehyde groups, dialdehydes, e. g., succindialdehyde, etc., apparently react with some sensitizing dyes added to photographic emulsions and cause them to lose their sensitizing action.

As man widely different embodiments of this invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not to be limited except as I defined by the claims.

What is claimed is:

1. A light-sensitive, gelatino silver-halide emulsion containing a small amount of 2,5-dimethoxytetrahydrofuran.

2. A light-sensitive, gelatino silver-halide emulsion containing from 0.2 to 3.3 parts of 2,5- dimethoxytetrahydrofuran per part of gelatin on a dry basis.

3. A photographic element comprising a thin flexible sheet support bearing at least one thin layer composed of a light-sensitive, gelatino silver-halide emulsion containing a small amount of 2,5-dimethoxytetrahydrofuran.

4. A photographic element comprising a thin flexible sheet support bearing at least one layer composed of a light-sensitive, gelatino silverhalide emulsion containing from 0.2 to 3.3 parts of 2,5-dimethoxytetrahydrofuran per part of gelatin on a dry basis and having a thin gelatin protective layer coated on said emulsion layer.

5. A photographic element comprising a thin flexible sheet of paper hearing at least one layer composed of a light-sensitive, gelatino silverhalide emulsion containing from 0.2 to 3.3 parts of 2,5-dimethoxytetrahydrofuran per part of gelatin on a dry basis and having a thin gelatin protective layer coated on said emulsion layer.

WILLIAM ALEXANDER STANTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 5 Number Name Date 2,172,300 Stand et al. Sept. 5, 1939 2,400,532 Blake May 21, 1946 

1. A LIGHT-SENSITIVE, GELATINO SILVER-HALIDE EMULSION CONTAINING A SMALL AMOUNT OF 2,5-DIMETHOXYTETRAHYDROFURAN.
 5. A PHOTOGRAPHIC ELEMENT COMPRISING A THIN FLEXIBLE SHEET OF PAPER BEARING AT LEAST ONE LAYER COMPOSED OF A LIGHT-SENSITIVE, GELATINO SILVERHALIDE EMULSION CONTAINING FROM 0.2 TO 3.3 PARTS OF 2,5-DIMETHOXYTETRAHYDROFURAN PER PART OF GELATIN ON A DRY BASIS AND HAVING A THIN GELATIN PROTECTIVE LAYER COATED ON SAID EMULSION LAYER. 